This invention relates to a semiconductor device and, in particular, to an electrode pad structure in a semiconductor device.
Generally, a great number of electrode pads are arranged around a semiconductor chip to connect the semiconductor chip with inner leads of a lead frame by wiring. Such electrode pads themselves become small in size and thin in thickness with an increase of integration of the semiconductor chip and tend to be arranged with a very small pitch around the semiconductor chip.
Under the circumstances, each electrode pad is liable to come off the semiconductor chip on bonding a metal wire, such as a gold wire, onto each electrode pad. This is because the electrode pads are deposited on an insulating layer formed on a semiconductor substrate and adhesion is not always good between the insulating layer and the electrode pads when glass and aluminum are used to the insulating layer and the electrode pads, respectively.
Japanese Unexamined Patent Publications (JP-A) No. Syo 60-227483, namely, 227483/1985 proposes a method of manufacturing a solar cell so as to prevent an aluminum layer from being peeled off. To this end, the method includes the steps of making a surface of a substrate coarse and depositing a solder film on the coarse surface.
However, no consideration is made at all about electrode pads of a semiconductor device.
It is an object of this invention to provide a semiconductor device which is capable of preventing each electrode pad portion from coming off a semiconductor chip.
A semiconductor device to which the present invention is applicable has a semiconductor substrate and a pad electrode portion formed on the semiconductor substrate through an insulation film. The insulation film has recesses at the pad electrode portion. The pad electrode portion comprises metal films buried in the recesses and an electrode pad film which is contacted with the metal films and which covers the insulation film.
Thus, the electrode pad portion according to the present invention is formed on the recessed insulation film to widen a contact area between the electrode pad portion and the insulation film. The metal films or metal portions may be formed by a refractory metal, such as tungsten, molybdenum.
In addition, a laminate may be placed under the electrode pad film and the metal portions to be contacted with the insulation film and may comprise an underlying film of, for example, Ti, and an intermediate film of, for example, TiN between the underlying film and each of the electrode pad film and the metal portions. With this structure, it is possible to prevent the underlying film and the insulation film from being peeled off by stress due to ultrasonic vibration given on bonding. This is because the underlying film of, for example, Ti has a portion which is vertically extended towards the surface of the substrate and which serves to withstand horizontal stress which results on bonding from the ultrasonic vibration horizontally traveling.